PHILIP GEORGE 



— 10.7 e.u., are themselves low when compared to the values for 

 ionic iron complexes; this can be attributed to a tightening of 

 the prosthetic group and possibly the nearby protein fabric 

 accompanying complex formation. Hence if the structure 

 tightens upon the entry of the first oxygen, and the configuration 

 of the hemoglobin molecule in fresh preparations is such that 

 this tightening influences the structure about the hemes which 

 have not yet reacted, then the same degree of tightening may not 

 be possible in the addition of the second, third, and fourth 

 oxygen molecules. A^" would thus be more positive for the last 

 oxygenation, and A//o more negative for the first because of the 

 stronger bonding— as is found experimentally. 



Some aspects of the kinetic data for these oxygenation re- 

 actions, however, suggest that the oxygenation of the fourth 

 heme parallels the myoglobin reaction (37), so additional data 

 on other hemoglobin reactions are very desirable for a more 

 thorough appraisal of the problem. In a very recent survey 

 (13a), which includes data for the hemoglobin-CO reaction, it 

 appears that even though there are great similarities between 

 the partial molal entropies of O2 and CO, and great similarities 

 between the physical properties of oxyhemoglobin and carbon- 

 monoxyhemoglobin, the trends in A//° and AS'^ given in Table 

 VII may be a unique feature of the oxygenation reaction. 



The Stability of Oxyhemoglobin and Oxymyoglobin* 



The oxygenation of myoglobin and hemoglobin has been 

 discussed so far only in relation to the formation of other hemo- 

 protein complexes, containing CO, F~, CN~, OH~, etc. But 

 the existence of these particular complexes as stable entities 



* In this section and the next, formulas are written with the charge on 

 the iron atom corresponding to ferrous and ferric ions, not according to the 

 net charge as before, so as to reveal more clearly the valency changes and 

 changes in oxidation state. The subscript p is used, denoting porphyrin, for 

 reactions common to several hemoproteins; subscripts Mb, Per, etc., are used 

 for particular myoglobin or peroxidase reactions, etc. 



366 



